Free-Falling Test Masses

LPF's geodesic test particles

The Gravitational Reference System

The LPF test masses are at once references of geodesic motion and mirrors for the optical interferometer metrology.

The LPF test masses are gold-coated cubes made from an Au-Pt alloy, with a side length of 46 mm, and a total mass of 1.97 kg. The material has been chosen first for its magnetic purity – this alloy is tuned to null the magnetic susceptibility that gives an induced dipole moment and allows near elimination of contaminants that give a permanent magnetic moment – and for its density, maximizing inertia to give the smallest possible accelerations for a given stray force. The entire TM is coated with gold, to ensure an homogeneous equipotential surface, that also serves as a mirror for the interferometry readout.